Spiral structures like the one pictured here could replace batteries in the future because they can store energy like a spring and conduct electricity. The structure is a tiny nanotube that consists entirely of carbon atoms. Carbon nanotubes are made in labs, but carbon-based compounds are also the most common naturally occurring compounds on Earth. More than 90 percent of all known compounds contain carbon. Do you know why carbon is found in so many compounds? Read on to find out. If you first want to learn more about carbon nanotubes, go to this URL: http://www.youtube.com/watch?v=oxD3vfg3Nd8

Carbon is a nonmetal in group 14 of the periodic table. Like other group 14 elements, carbon has four valence electrons. Valence electrons are the electrons in the outer energy level of an atom that are involved in chemical bonds. The valence electrons of carbon are shown in the electron dot diagram in the Figurebelow.

A: Carbon needs four more valence electrons, or a total of eight valence electrons, to fill its outer energy level. A full outer energy level is the most stable arrangement of electrons.

Q: How can carbon achieve a full outer energy level?

A: Carbon can form four covalent bonds. Covalent bonds are chemical bonds that form between nonmetals. In a covalent bond, two atoms share a pair of electrons. By forming four covalent bonds, carbon shares four pairs of electrons, thus filling its outer energy level and achieving stability.

How Carbon Forms Bonds

A carbon atom can form covalent bonds with other carbon atoms or with the atoms of other elements. Carbon often forms bonds with hydrogen. Compounds that contain only carbon and hydrogen are called hydrocarbons. Methane (CH4), which is modeled in the Figurebelow, is an example of a hydrocarbon. In methane, a single carbon atom forms covalent bonds with four hydrogen atoms. The diagram on the left in the Figurebelow shows all the shared valence electrons. The diagram on the right in the Figurebelow, called a structural formula, represents each pair of shared electrons with a dash (–).

Methane (CH4)

Carbon-Carbon Bonds

Carbon can form single, double, or even triple bonds with other carbon atoms. In a single bond, two carbon atoms share one pair of electrons. In a double bond, they share two pairs of electrons, and in a triple bond they share three pairs of electrons. Examples of compounds with these types of bonds are represented by the structural formulas in the Figurebelow.

Q: How many bonds do the carbon atoms share in each of these compounds?

A: In ethane, the two carbon atoms share a single bond. In ethene they share a double bond, and in ethyne they share a triple bond.

Summary

Carbon forms covalent bonds with atoms of carbon or other elements. There is a great diversity of carbon compounds, ranging in size from just one to thousands of atoms.

Carbon has four valence electrons, so it can achieve a full outer energy level by forming four covalent bonds. When it bonds only with hydrogen, it forms compounds called hydrocarbons.

Carbon can form single, double, or triple covalent bonds with other carbon atoms.

Practice

Read the article about carbon bonding at the following URL, and then make an outline of article content.